The present invention relates generally to rotary synchronous machines having field and armature windings provided on a stator, and more particularly to a rotary synchronous machine capable of optionally controlling thrust developed in an axial direction of a rotation shaft.
Synchronous motors are available in a variety of designs, such as the rotating-armature, rotating-field and inductor types. The rotating-armature type synchronous motors comprise a magnetic field pole provided on a stator, and an armature winding provided on a rotor. The rotating-field type synchronous motors comprise an armature winding provided on a stator, and a magnetic field pole provided on a rotor. The magnetic field pole in the rotating-field type synchronous motors is typically a permanent magnets positioned on the rotor, or a magnetic field winding that is excited by direct current. Further, the inductor-type synchronous motors comprise a magnetic field pole and an armature winding provided on a stator, and an inductor provided on a rotor and having gear-like teeth and slots.
Since the armature winding is provided on the stator as mentioned, the rotating-field type synchronous motors are substantially free from mechanical damages and breakage and permit easy insulation, so that they are widely used today as drive means for rotating the spindles of various machine tools and others.
However, such rotating-field type synchronous motors where the field pole comprises a permanent magnet positioned on the rotor are disadvantageous in that the permanent magnet itself is expensive and must be secured firmly enough to not accidentally detach from the rotor and also in that it is difficult to provide large capacity because the magnetic field produced is always constant. The rotating-field type synchronous motors where the field pole comprises a magnetic field winding provided on the rotor are also disadvantageous in that they essentially require slip rings and a rotary transformer in order to supply field current to the rotor, resulting in a complex structure.
The rotary drive means do not produce a thrust in an axial direction thereof although they give rotational force, i.e., torque. Therefore, in cases where both rotational force and axial thrust are required, it has been customary to provide a linear drive means separate from the rotary drive means, so as to control the rotational force and axial thrust by the different drive means. However, because at least two separate drive means were necessary for the control of the rotational force and axial thrust, a relatively large space was required. Thus, in most cases, it has been conventional for the entire rotary drive means to be controlled by the linear drive means.
It is therefore an object of the present invention to provide a thrust-controllable rotary synchronous machine which is, by itself, capable of simultaneously controlling both rotational force and axial thrust.
In order to accomplish the above-mentioned object, the present invention provides a rotary synchronous machine which comprises: a stator; an armature core provided on the stator and having armature windings sequentially wound thereon in a direction of rotation; a rotor including a plurality of magnetic substance segments which are magnetically coupled with the armature core but are magnetically separated from each other in the direction of rotation; and a magnetic field core that is provided on the stator in magnetically-separated relation to the armature core but is magnetically coupled with the armature core via the rotor, the magnetic field core having field windings positioned thereon for producing rotating magnetic poles and thus providingducing, in the rotor, an axial thrust corresponding to intensity of electric currents passed through the field windings.
On the stator, the magnetic field core and armature core are magnetically separated from each other. On the rotor, a plurality of magnetic substance segments are magnetically separated from each other in a direction of rotation but are magnetically coupled with both of the magnetic field core and armature core. Thus, N and S rotating magnetic poles produced on the magnetic field core are coupled together via the rotor and armature core, to form closed magnetic circuitry. Because the rotor and armature core are coupled in a direction normal to the rotation axis, magnetic attraction between the rotor and armature core will contribute only to rotational force. The rotor and magnetic field core, on the other hand, are arranged to cause an axial thrust to the rotor depending on the intensity of the electric currents passed through the filed windings. Namely, the rotor and magnetic field core are arranged in such a manner that magnetic attraction (magnetic coupling) occurs between the rotor and the magnetic field core in a same direction as the rotational axis or at a predetermined non-normal angle relative to the rotational axis. Thus, thrust is produced based on the magnetic attraction between the rotor and the magnetic field core, and this thrust corresponds to the intensity of the electric currents passed through the field windings. Consequently, a traveling position of the rotor in the axial direction can be controlled by providing the magnetic field cores adjacent to opposite sides of the rotor and appropriately controlling the intensity of the field currents.
According to another aspect of the present invention, there is provided a rotary synchronous machine which comprises: a stator; a cylindrical armature core provided along an inner surface of the stator and having armature windings that extend along a direction of rotation and are sequentially received in slots formed radially in the armature core; a rotor including a plurality of cylindrical magnetic substance segments that are magnetically coupled with the inner surface of the armature core but are magnetically separated from each other in the direction of rotation; a first magnetic field core that is provided on the stator in magnetically-separated relation to the armature core but is magnetically coupled with one side surface of the cylindrical magnetic substance segments of the rotor, the first magnetic field core having field windings positioned thereon for producing rotating magnetic poles; a second magnetic field core that is provided on the stator in magnetically-separated relation to the armature core but is magnetically coupled with another side surface of the cylindrical magnetic substance segments of the rotor, the second magnetic field core having field windings positioned thereon for producing rotating magnetic poles; and a current control device that controls intensity of electric currents to be supplied to the first magnetic field core and second magnetic field core, to thereby control an axial thrust of the rotor. In this rotary synchronous machine, a pair of the magnetic field cores are provided adjacent to opposite sides of the rotor, and the axial thrust of the rotor is controlled by the current control device controlling the intensity of the currents passed through the two magnetic field cores.
In a preferred implementation of the present invention, a cylindrical permanent magnet is provided around an outer peripheral surface of the cylindrical magnetic substance segments of the rotor. If the surface of the cylindrical permanent magnet opposed to the rotor is excited to assume the S pole and the surface of the magnet opposed to the armature core is excited to assume the N pole, the surfaces of the magnetic substance segments opposed to the first and second magnetic field cores are excited to assume the S pole; conversely, if the surface of the cylindrical permanent magnet opposed to the rotor is excited to assume the N pole and the surface of the magnet opposed to the armature core is excited to assume the S pole, then the surfaces of the magnetic substance segments opposed to the first and second magnetic field cores are excited to assume the N pole. Thus, the rotor is caused to rotate in response to the electric currents passed through the armature windings even when no field currents are supplied. Then, both the rotational force and the axial thrust can be controlled by controlling the intensity of the field currents. In this case, the axial thrust can be controlled finely by causing the field currents, to be supplied to the first and second magnetic filed cores, to be in phase with each other and producing magnetic attraction between the, first and second magnetic filed cores and the rotor. Further, the axial thrust can be controlled greatly by causing the field currents, to be supplied to the first and second magnetic filed cores, to be in opposite phase and producing magnetic attraction between the first magnetic field core and the rotor while producing magnetic repulsion between the second magnetic field core and the rotor.
In another preferred implementation, the cylindrical permanent magnet of the rotor is tapered at least one end portion thereof to provide a conically slanted surface and the first magnetic field core and second magnetic field core are provided to be magnetically coupled with the conically slanted surface of the rotor. By thus tapering the rotor, a sufficient traveling distance of the rotor greater than a gap between the magnetic substance segments and the magnetic field cores can be guaranteed even through the gap width is small, and it is possible to reduce the necessary field currents and substantially improve the thrust characteristics.
According to still another aspect of the present invention, there is provided a rotary synchronous machine which includes a plurality of improved rotary synchronous machine structures connected together along an axis of a same rotation shaft, and each of the improved rotary synchronous machine structures comprises: a stator; an armature core provided on the stator and having armature windings sequentially wound thereon in a direction of rotation; a rotor including a plurality of magnetic substance segments which are magnetically coupled with the armature core but are magnetically separated from each other in the direction of rotation; and a magnetic field core that is provided on the, stator in magnetically-separated relation to the armature core but is magnetically coupled with the armature core via the rotor, the magnetic field core having field windings positioned thereon for producing rotating magnetic poles and thus causing, to the rotor, an axial thrust corresponding to intensity of electric currents passed through the field windings. This multi-stage arrangement can produce a sufficiently great axial thrust.